In normal production of pneumatic tires, the extruded tread consists of only two compound parts, i.e. the cap and the base compound. Sometimes a calendared cushion is put on the base compound to avoid tack problems in tire building.
EP 1 398 182 A2 discloses a tire having a multi-layered tread. In detail, the respective tire comprises a tread base layer, an intermediate layer, and a cap layer comprising lugs and grooves. The tread cap layer comes into contact with the road, wherein the intermediate layer extends to and includes a visible bottom portion of said grooves in said cap layer. Furthermore, said intermediate layer is comprised of a carbon black-rich rubber compound. However, the intermediate layer is not intended to contact the street upon normal wear of the tire.
Document U.S. Pat. No. 5,176,765 discloses a pneumatic tire having an outer tread layer of foam rubber in order to prevent crack occurrence at groove bottoms. Furthermore, the tread shall improve tire performances for both summer and winter. In accordance with this publication, the tread portion is composed of an outer foam rubber layer and an inner ordinary layer, whereas the hardness of the inner rubber layer is higher than the hardness of the outer rubber layer so that it is possible to reduce on the one hand a change in groove width after vulcanization and on the other hand dynamic strain concentration during travel in this region.
Document EP 1 630 003 A1 discloses a heavy-duty pneumatic tire and a method of producing the same preventing the occurrence of wrinkles and cracks on groove bottoms of the main grooves. The tread of the tire comprises a cap layer disposed on an outermost side in a radial direction of the tire and radially below the cap layer a middle layer and yet below the middle layer the tread base layer. In accordance with this tire all three layers extend essentially over the complete axial width of the tread, i.e. from the inner shoulder region of the tire to the outer shoulder region of the tire.
In view of the above cited prior art still room for improvement remains. In particular, it would be favorable to adapt the tread even better to performance or durability requirements.